Post-focal filamentation of an externally focused femtosecond laser pulse in air

Self-focusing and filamentation of externally focused ultrashort laser radiation in air are discussed. The influence of initial beam focusing on the filamentation length is numerically studied, and the conditions under which a light filament can resurrect after the linear focus are determined. We have found that the probability of this post-focal filamentation increases with an increase of laser power regardless of the type of filamentation (single/multiple).